Journal of Climate, 23, 8611-8629.
Nicolas Rochetin, Benjamin R. Lintner, Kirsten L. Findell, Adam
H. Sobel, and Pierre Gentine
Abstract
Radiative-convective equilibrium (RCE) describes an idealized atmosphere in which the vertical temperature distribution is determined by a balance between radiative and convective fluxes. While RCE has been applied extensively over oceans, its application to land has been limited. The present study explores the properties of RCE over land surfaces, using an atmospheric single column model (SCM) from the Laboratoire de Meteorologie Dynamique (LMD) General Circulation Model (LMDZ5B) coupled in temperature and moisture to a land surface model. Given the presence of a large amplitude diurnal heat flux cycle, the inclusion of land surface hydrology, and the finite moisture capacity of the surface, the resultant RCE exhibits multiple equilibria when conditions are neither water- nor energy-limited. By varying top-of-the-atmosphere insolation (latitude), total water content, and initial temperature conditions, the sensitivity of the LMDZ5B land region RCE is assessed, with an emphasis on the role of clouds. The presence or absence of low-level clouds and fog as well as the diurnal cycle are required for the existence of multiple equilibria, and have a leading-order impact on the equilibrium states since they strongly modulate the diurnal evolution of surface heating. In addition the simulated surface precipitation rate varies non-monotonically with latitude as a result of a tradeoff between cloud-base rain rate and rain re-evaporation, thus underscoring the importance of subcloud layer processes and unsaturated downdrafts. Overall this analysis suggests the key role of the diurnal evolution of the boundary layer and of low-level clouds over land.